wifi: mt76: mt7915: fix potential tx_retries underflow

When FIELD_GET returns 0 for the retry count, subtracting 1 causes
an unsigned integer underflow, resulting in tx_retries becoming a
very large value (0xFFFFFFFF for u32).

Fix by checking if count is non-zero before subtracting 1.

Fixes: 943e4fb96e6f ("wifi: mt76: mt7915: report tx retries/failed counts for non-WED path")
Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
Link: https://patch.msgid.link/20260605113306.3485554-1-ryder.lee@mediatek.com
Signed-off-by: Felix Fietkau <nbd@nbd.name>

diff --git a/drivers/net/wireless/mediatek/mt76/mt7915/mac.c b/drivers/net/wireless/mediatek/mt76/mt7915/mac.c
index cec2c4208255fd30ef2d4db390681a15719f5ef3..334c19ab2b22ca4e6c994c5178b15c9de34530fe 100644 (file)
--- a/drivers/net/wireless/mediatek/mt76/mt7915/mac.c
+++ b/drivers/net/wireless/mediatek/mt76/mt7915/mac.c
@@ -912,16 +912,16 @@ mt7915_mac_tx_free(struct mt7915_dev *dev, void *data, int len)
                }
 
                if (!mtk_wed_device_active(&mdev->mmio.wed) && wcid) {
-                       u32 tx_retries = 0, tx_failed = 0;
+                       u32 tx_retries = 0, tx_failed = 0, count;
 
                        if (v3 && (info & MT_TX_FREE_MPDU_HEADER_V3)) {
-                               tx_retries =
-                                       FIELD_GET(MT_TX_FREE_COUNT_V3, info) - 1;
+                               count = FIELD_GET(MT_TX_FREE_COUNT_V3, info);
+                               tx_retries = count ? count - 1 : 0;
                                tx_failed = tx_retries +
                                        !!FIELD_GET(MT_TX_FREE_STAT_V3, info);
                        } else if (!v3 && (info & MT_TX_FREE_MPDU_HEADER)) {
-                               tx_retries =
-                                       FIELD_GET(MT_TX_FREE_COUNT, info) - 1;
+                               count = FIELD_GET(MT_TX_FREE_COUNT, info);
+                               tx_retries = count ? count - 1 : 0;
                                tx_failed = tx_retries +
                                        !!FIELD_GET(MT_TX_FREE_STAT, info);
                        }